1. Field of the Invention
The present invention relates to an optical apparatus for measuring surface topography of an object, and in particular to an apparatus which uses the blockage of a coherent light source to measure the relative or absolute size, shape, position, orientation, cross-sectional circumference or area, volume, surface topography, or specific volume (percent body fat) of a human body or other object.
2. Discussion of the Prior Art
There are an enormous number of applications in which it is desirable to have a non-contact method of measuring the contours of a body or object. Examples of some of these applications and their prior art solutions can be found in U.S. Pat. Nos. 4,406,544, 4,679,076, and 5,072,121 (measuring the human body for various-medical purposes), 3,880,289 and 4,693,607 (measuring vegetables and fruit for sorting), and 3,905,705, 4,192,613, 4,198,165, 4,417,817, 4,877,970, 4,905,512, and 5,142,159 (measuring various objects for industrial purposes.) These methods and apparatuses have limited uses and have drawbacks such as excessive size, complexity, cost, and measurement time.
There are other applications in which the measurement of contours or volume is not performed, but would be if more practical. For example, when a person is dieting to improve his or her appearance and wishes to "lose weight", losing volume is actually what that person is most concerned with. The measure of weight has only been used because it has been much more accurate, practical and inexpensive to measure one's weight than one's volume with traditional measurement methods. The measurement of one's volume is actually a better indicator of diet progress, and has the advantage of indicating exactly how much fat, muscle, water, etc. is being gained or lost in particular areas of the body. "Body builders" and those dieting strictly for health reasons are also concerned with volume. These people, as well as traditional dieters, are concerned with adding muscle and losing fat. Accurately measuring the percentage of body fat on a person involves measuring both weight and volume. Percent body fat is a variation of specific volume, which is the volume measured per unit of weight. Traditional methods of measuring a person's volume for this purpose involve measuring water displacement or a person's weight while he or she is submerged under water. Other methods of approximating the amount of body fat include pinching different areas of a person with special calipers to measure the thickness of the flesh. These methods are complicated, inconvenient, and not always very accurate. If the measurement of body volume and body fat were more accurate, convenient, and less expensive, more people might be inclined to take these measurements more often.
Measuring external body changes during pregnancy may be another area that could benefit from an improved measuring system. Currently, weight gain is often tracked during pregnancy, but unless the physician is also using a tape to measure various circumferences of the woman's body, a weight measurement provides very little information as to what type and where the weight is being gained. In other words, it is difficult to accurately determine whether a particular increase in weight is due to retained water, the addition of fat, an increase in the mass of the fetus, and/or some other factor.
Chiropractic care is another area in which accurately measuring the surface topography of the human body would be beneficial. Currently, gauges, scales and other special equipment are used to measure body alignment. This equipment is often complicated and time consuming to use, producing inaccurate results. X-rays are used to locate the skeletal structure more accurately, but taking x-rays, developing the film, and interpreting the results are also difficult and time consuming. X-ray equipment is expensive, and problems associated with over-exposing a patient to x-rays prevents this technology from being used more frequently.
Industrial and commercial areas that would benefit from an improved method of measuring objects include industries that scan objects for computer aided design, analysis and manufacturing work (CAD/CAM and Finite Element Analysis), prototyping and replicating with stereo lithography, and building large stage props, models or virtual reality data bases. Custom clothing industries could measure and transmit accurate information about a client's shape and size. Water content and volume of poultry or produce could be readily measured in the field. There are also countless quality control and sorting tasks that could take advantage of an improved surface measurement device.
Referring to FIG. 1, an example of the shortcomings of prior art measuring devices can be seen by considering one of the patents listed above. U.S. Pat. No. 3,905,705, entitled OPTICAL MEASURING APPARATUS, discloses a laser device for measuring dimensions on small objects, and which has been successfully commercialized by Techmet Company of Dayton, Ohio. According to the prior art invention, a laser beam is reflected off of a rotating mirror to produce a rotary scanning light beam. The rotary scanning beam passes through a converging lens to create a parallel scanning light beam. The parallel scanning light beam then passes through a second converging lens which focuses the scanning beam onto a photo-detector. When an object to be measured is placed in the parallel scanning light beam between the two lenses, it creates a shadow on the detector during a portion of the beam's scan. By measuring the duration of this shadow, the thickness of the object can be determined.
The prior art device is easy to use, quick, highly accurate, and makes a non-contact measurement using relatively few parts. However, the size of the object that can be measured is limited by the size of the two lenses, which must be larger than the object. The device also is only able to measure one dimension of the object. To measure the entire surface of a large object, such as a human body, the diameter of the two lenses would have to be greater than the width of the person, and the entire apparatus would have to rotate around the person and also traverse the height of the person. (The proposed apparatus would have the scanning beam in a horizontal plane, rather than in a vertical plane as shown in FIG. 1.) Alternatively, the person could be rotated while being raised through the parallel scanning beam. Either way, the proposed apparatus would be prohibitively large, slow and expensive. Other prior art devices have similar shortcomings, such as excess cost and complexity.
What is needed, and is not provided by the prior art, is a relatively simple and cost effective, non-contact measuring device that can quickly and conveniently measure the surface topography of an object, large or small.